A variety of processes have heretofore been known for producing silicon that is used as a starting material of semiconductors or wafers for solar power generation, and some of them have already been put into practice on industrial scales. For instance, one of them is a process called Siemens process in which silicon core members arranged in a reaction vessel are heated by flowing an electric current thereto to a temperature at which silicon deposits, a gas of a silane compound such as trichlorosilane (SiHCl3) and a hydrogen gas are fed therein so that silicon is formed by the reducing reaction, and the formed silicon is deposited on the silicon core members. This process has a feature in that polycrystalline silicon of a high purity is obtained in the form of rods, and has been put into practice as the most general process (see patent documents 1, 2).
There has, further, been proposed a process for preventing the dichlorosilane in the discharge gas from being converted into the tetrachlorosilane by quenching the discharge gas from a bell jar from 1000° C. down to not higher than 800° C. in not longer than 0.2 seconds (see patent document 3).